1. Field of the Invention
The present invention relates to a structural arrangement for radio communication terminals.
2. Description of the Prior Art
The current trend is to produce radio communication terminals of small size that are functionally ergonomic and user friendly. A radio communication terminal mainly comprises a casing in which equipment units are housed, in particular a radio transceiver unit comprising at least an antenna and a man-machine interface unit generally including a keypad, a screen and a sound transducer.
The search for improved ergonomics and convenience has led to the antenna being accommodated inside the casing, for example, through the development of planar patch antennas. The same trend is encouraging the provision of increasingly comprehensive and increasingly larger man-machine interfaces.
FIG. 1 shows diagrammatically the various component parts of a radio communication terminal. This kind of terminal generally comprises a casing 10 made of a rigid insulative material or partly of metal and in which are disposed various components connected to a printed circuit card 100. The terminal comprises at least a screen 20, a keypad 25, a battery 27, an antenna 40 for establishing radio communication, and a transducer 30 for reproducing sound able to transform electrical signals supplied to it into sound waves.
The sound transducer 30 can have a number of functions, such as those of an earpiece, a loudspeaker and a ringer. The earpiece is essentially intended to be placed against the ear of a user when using the device to communicate, the ringer alerts the user to an incoming call or some other action, and the loudspeaker provides sound reproduction at a high volume, for example for hands-free applications. To reproduce the sound waves, the sound transducer 30 uses two separate acoustical resonance volumes respectively defining a front acoustical cavity 31 and a rear acoustical cavity 32 whose shapes and dimensions are chosen to achieve sound reproduction of sufficient quality for the application for which the transducer is intended. In particular, the size of the transducer 30 and the dimensions of the front and rear acoustical cavities 31 and 32 define the spectrum and the sound pressure level of the transducer. A rear cavity that is too small limits the sound spectrum at low frequencies, which reduces the sound pressure level at the bottom end of the spectrum.
FIG. 2 shows diagrammatically a sound transducer. In the conventional way, a transducer 30 includes a vibrating membrane 33 secured by attachments to the walls of a diaphragm 34 so as to be able to vibrate freely when acted on by a coil 37, to which it is attached, which is in turn caused to vibrate by a magnet 38 disposed on a metal support 39, such as a yoke.
Theoretically, the earpiece function necessitates a smaller component than a loudspeaker and ringer function, which must produce a higher sound volume. The volume used by a sound transducer 30 can be defined as the volume occupied by the component itself and the volume occupied by the acoustical cavities previously defined. The volume for correct operation of the transducer cannot be reduced below a particular limit imposed by the loudspeaker function.
As previously mentioned, the current trend is to enlarge the man-machine interface and in particular the screen, for example through the use of liquid crystal screens. Because the size of the keypad cannot be reduced, for reasons of convenience of use, the present invention proposes to use the space occupied by the sound transducer to enlarge the space available to receive a screen without reducing the size of the keypad or increasing the size of the mobile terminal.
The object of the invention is to eliminate the drawbacks of the prior art.
To this end, the invention proposes to retain only a simple earpiece on the front face of the terminal and to transfer the loudspeaker and ringer function to the rear of the terminal. To guarantee a good quality of sound reproduction, the rear acoustical cavities of the two transducers constituting the earpiece and the loudspeaker, communicate with each other. This feature is referred to hereinafter as a twin rear acoustical cavity.